My TV has only NTSC, ATSC, QAM tuners. I'm moving to India where the
standard is PAL. What do I need to do for it to work there? It has
been suggested that some cable set-top boxes available in India have
NTSC outputs. But I'm not certain this  solution works. I'd like a
guaranteed solution.

The guaranteed solution is to sell your TV in North America.

The NTSC vertical scanning frequency is 60 Hz, whereas the television
system in India is certainly similar to that in Europe which has a
vertical scanning frequency of 50 Hz.

Hence your TV would not be compatible for that reason (together with
all the other reasons such as channel frequencies and colour system
incompatibility).

What about PAL-NTSC converters like this one:
http://www.amazon.com/Atlona-Multi-system-ntsc-Video-Converter/dp/B000HJGDWS/sr=8-1/qid=1160694393/ref=pd_bbs_1/102-3531116-6136158?ie=UTF8
?